This invention relates to the field of electrically driven lighting, to means for driving one or more lamps using inductive power transfer, and more particularly but not exclusively to the provision of emergency lights, indicating lights, and roadway signal lighting powered from adjacent concealed cables.
Transmission of electrical power to articles which consume power over significant gaps by means of inductive power transfer has become increasingly feasible with developments in resonant primary and resonant secondary conductors, means to control and limit the resonant secondaries, and suitable energising power supplies.
There are a number of applications where even a fixed source of light is advantageously driven by an inductively powered source, rather than by simple direct connections using conductive materials.
In most of the situations below, some of which are particularly adverse for conventional lighting, a particularly reliable lighting source is an advantage and in most of these situations the nature of inductive powering of lights will inherently enhance the reliability of a system over that using alternative power supplies such as direct connections, internal batteries, or solar cells with rechartable batteries. Some situations include:
where electrical isolation is necessary, as in lights used in or near water such as in swimming pools or areas where people work in contact with water,
where corrosive or conductive fluids are likely to occur,
where sparks may cause explosions, as in coal mines and in operating theatres or in certain other industrial sites where flammable powders, gases, or the like are found,
where the added robustness of buried cables assists in maintaining power transfer during exceptional circumstances,
where a surface on which lights are laid is prone to be replaced, such as on a roadway with a tar sealed surface.
In our U.S. pat. 5,293,328 we describe an inductive power transfer system having particular application to a multiplicity of vehicles.
It is an object of the present invention to provide an improved system for the inductive transfer of electrical energy to a source of light or one which will at least provide the public with a useful choice.
In one aspect the invention provides an inductively powered lamp unit; the lamp unit including one or more lamps capable of radiating light and comprising means to
collect inductively transferred power from an external alternating primary magnetic field; said collection means comprising a resonant circuit having a resonant period and including at least one inductance and at least one capacitance; wherein the at least one inductance has a winding adapted to be intersected by a portion of the alternating magnetic field and thereby collect power as a secondary current, means capable of limiting the maximum amount of secondary current circulating in the resonant circuit, means to transfer power at an output from the resonant circuit to the lamp or lamps,
and means to control the power provided to the lamp or lamps.
Preferably the means capable of limiting the amount of secondary current circulating in the resonant circuit comprises a shorting switch capable of closing a connection across the inductance; the shorting switch being controlled by a controller provided with means capable of sensing the magnitude of the output so that when the output exceeds a first, higher, predetermined threshold the shorting switch is closed for a period exceeding the resonant period of the circuit, or when the output falls below a second, lower, predetermined threshold the shorting switch is opened;
thereby limiting the secondary current flowing in the resonant circuit so that any magnetic flux generated by the secondary current does not have a significant counteracting effect on the primary field and so that the output of the resonant circuit is not able to exceed a predetermined maximum.
Preferably the means capable of sensing the magnitude of the output is configured so as to sense an output current.
Alternatively the means capable of sensing the magnitude of the output is configured so as to sense a relative or absolute output light intensity.
Preferably the resonant inductance comprises one or more coils, each coil being wrapped around an elongated member composed of a ferromagnetic material having a midpoint, which member is orientated when the lamp unit is placed in position so as to lie with its midpoint substantially adjacent to a primary conductor (capable when energised of radiating a primary field), and substantially at right angles to the direction of the primary conductor.
Preferably the lamp unit has a low profile and at least one window capable of transmitting light; the unit being capable of being attached to the surface of a roadway; and wherein the lamp or lamps comprise one or more light-emitting diodes.
It is also preferable that the lamp unit is packaged in a strong housing having a low profile and at least one window capable of transmitting light; the unit being capable of being attached onto the surface of a roadway, capable of withstanding loads applied by a road vehicle driving over it, and not capable of adversely affecting the integrity of the road vehicle nor deflecting the road vehicle from its course.
Preferably the lamp unit also includes at least one retroreflector unit for passively reflecting the light of vehicle beams.
In another aspect the invention provides a lighting installation comprising one or more inductively powered lamp units as described above, each affixed to a surface of a substrate, each lamp unit being capable of emitting light on being energised by inductive transfer of power across a space from a primary conductor located beneath the surface of the substrate; the primary conductor carrying, when in use, an alternating current.
Preferably the primary conductor radiates an external alternating magnetic field, at a frequency which is substantially the same as the resonant circuit in at least one of the lamp units; the frequency lying in the range of between 200 Hz and 2 MHz.
Preferably the primary conductor is laid down within a substrate in the topology of a loop, connected at a first open end to a power supply and having a second, closed end, the loop comprising a pair of closely spaced conductors, though spread apart in an axis substantially perpendicular to the surface of the substrate at each site where a lamp unit is to be placed.
Preferably the one or more inductively powered lamp units are placed upon the substrate so as to guide a moving person (whether on foot or steering a vehicle) to pass along a particular route.
Preferably one or more lamp units may be selectively addressed using the primary conductor as a medium, so that the light radiated therefrom may be changed from time to time.
Preferably selective addressing is accomplished by superimposing a message over the primary current, in the form of momentary variations of the amplitude of the primary current.
Preferably selective addressing is accomplished by superimposing a message over the primary current, in the form of momentary variations of the phase of the primary current.
Preferably selective addressing is accomplished by superimposing a message over the primary current, in the form of information carried within a carrier frequency, separate from the frequency of the power for inductive transfer.
Preferably selective addressing is accomplished by setting the frequency of the primary current so as to match the resonant frequency of the resonant circuit of the addressed one or more lamp units which, for this purpose, may each be provided with one of a variety of resonant frequencies.
In another aspect the invention provides an installation for laying out marking lights on a road, comprising a set of inductively powered roadway markers, a primary energising loop cable, and a power supply.
Preferably the power supply is capable of energising the primary energising loop in response to an external triggering event.
Preferably the power supply is capable of remotely controlling one or more lamp units by means of the primary energising loop.
Preferably the power supply is capable of remotely controlling one or more lamp units by means of the primary energising loop in response to an external triggering event.
In another aspect the invention provides an installation for laying out marking lights along a fire escape route or egress route in relation to a building, comprising a set of inductively powered lamp units, a primary energising loop cable capable of being buried within a substrate of the building, and a power supply having a battery backup; the installation being capable of being activated during an emergency.
Preferably the primary alternating current is a sine wave.
Preferably it has a frequency in the range of from 500 Hz to 1 MHz, although more preferably it has a frequency in the range of from about 10 KHz to about 50 KHz.
Preferably the alternating current is generated within a resonant power converter.
Preferably the concealed primary cable is electrically insulated and mechanically protected by being embedded within the substrate. Optionally it may be sealed into a slit cut into the substrate with a circular saw or the like.
Preferably the concealed cable comprises a pair of conductors orientated substantially perpendicular to the surface of the substrate, although optionally a pair of conductors may lie side by side within parallel slits. Preferably the cable is composed of a litz wire or other wire having a high surface-to-volume ratio such as a strip.
In another aspect the invention provides a lamp unit within a strong housing, comprising a resonant secondary or pickup coil and capacitor, one or more light-emitting lamps, and optionally power conditioning means.
Optionally the lamp unit has a low profile and may be applied to a road surface.
Optionally the lamp unit also contains one or more retro-reflector modules.
Preferably the power conditioning means comprises a current limit and optionally this may be built into light-emitting diodes or be an intrinsic property of metallic filament lamps.
In the case of light-emitting diodes, a pair of lamps or of banks of lamps may be connected in inverse parallel in order to utilise both half-cycles of an AC waveform.
In a further aspect the invention may provide a road-markings set of lamps comprising a series of lamp units, an embedded cable, and a power supply.
Optionally this invention may be used to highlight dangerous portions of a highway.
Optionally it may be energised by the proximity of a vehicle.
In a related aspect the invention provides a pedestrian crossing, comprising means to detect the presence of a waiting pedestrian, sets of road markings, and a sequencer to energise the road markings lamps for a period of time before signalling to the pedestrian that a warning has been given.
In a yet further aspect the invention may provide a fire escape indication set of lamps.
Preferably the power supply for the invention is driven from a set of storage batteries so that it can operate in the at least temporary absence of a mains supply.